The present invention generally relates to box-making machinery wherein a plurality of blanks or boards or sheets are successively fed along a horizontal path to stations along the path where various operations are performed, for example, printing, cutting, slotting, folding, gluing, etc. More specifically, the present invention relates to methods and apparatus for successively feeding the boards or sheets to a pair of nip rolls which then feed the boards to the stations where the various above-indicated operations are performed.
There, of course, exists in the prior art various box-making machines including feeding mechanism for successively feeding the boards to nip rolls preliminary to the box-making operations to be performed on the boards. One conventional feeding mechanism referred to in the art as a "kicker feed" utilizes a reciprocating pusher bar which engages the rear or trailing edge of the board and pushes the board to the nip rolls. Once the board is engaged by the nip rolls, the pusher bar is returned to its starting position to engage the next board and push it to the nip rolls. The pusher bar is reciprocated through a rocker shaft which is driven from the main power source of the machine. Examples of such kicker feed mechanisms are disclosed in U.S. Pat. Nos. 3,392,973, 3,588,093 and 3,588,095.
Although a kicker feed mechanism has the advantage of being driven through a rocker shaft system which is relatively inexpensive, reliable and capable of providing high torque outputs as may be needed, it is thought by some to possess certain problems from the standpoint of safety and operation. For example, with a kicker feed, the kicker bar or pusher must be carefully controlled in order to squarely feed the blank in proper registry with the nip rolls. Moreover, the trailing edge of the sheet or board being fed must be carefully controlled to insure proper engagement with the feed lips of the kicker bar. Also, if the board or sheet is warped, it may become jammed due to the rear edge feed. Additionally, thin or low-strength sheets may not be able to withstand the column loading applied by the kicker bar.
In an attempt to avoid the above problems with kicker feeds, another type of feed, namely a "rotary feed", has been developed and used in industry. By way of example, it is noted that rotary-type feeders are disclosed in U.S. Pat. Nos. 4,363,478, 4,045,015, 976,640 and 978,702. With a rotary-type feed, the sheet or board is engaged by underlying rotating members or endless belts and is fed thereby to the nip rolls adjacent the leading edge area of the sheet. Such feeding obviates the rear edge feeding problems of kicker feeds while also utilizing a simple vacuum system to hold the board down on the feed members. One drawback, however, of a rotary feed system is that heretofore it has required the use of an indexing or geneva-type drive for driving the feed members, which drive is more complicated, expensive and possesses less torque capability than the rocker shaft system used with kicker feeds. The torque capacity of the drive limits the surface area of the rotary feed members which affects the engagement and consequently the feeding of the boards in the manner desired. Moreover, an indexing or geneva drive is not as versatile as a rocker shaft drive in adapting to various torque requirements of different box making or other machines.
Another problem which has attended various feed mechanisms of the prior art including kicker feeds or rotary-type feeds is that the leading edges of the sheets or boards at times become jammed against the gate at which they are stacked, making it difficult to lower the sheet onto the support surface for conveyance by the feed mechanism to the nip rolls.